diff --git a/mitmproxy/script/reloader.py b/mitmproxy/script/reloader.py
index b4acf51b4..99ce7f601 100644
--- a/mitmproxy/script/reloader.py
+++ b/mitmproxy/script/reloader.py
@@ -1,7 +1,7 @@
 import os
 import sys
 from watchdog.events import RegexMatchingEventHandler
-if sys.platform == 'darwin':
+if sys.platform == 'darwin':  # pragma: no cover
     from watchdog.observers.polling import PollingObserver as Observer
 else:
     from watchdog.observers import Observer
@@ -14,8 +14,8 @@ _observers = {}
 def watch(script, callback):
     if script in _observers:
         raise RuntimeError("Script already observed")
-    script_dir = os.path.dirname(os.path.abspath(script.args[0]))
-    script_name = os.path.basename(script.args[0])
+    script_dir = os.path.dirname(os.path.abspath(script.filename))
+    script_name = os.path.basename(script.filename)
     event_handler = _ScriptModificationHandler(callback, filename=script_name)
     observer = Observer()
     observer.schedule(event_handler, script_dir)
diff --git a/test/mitmproxy/script/test_reloader.py b/test/mitmproxy/script/test_reloader.py
new file mode 100644
index 000000000..af0ab88fd
--- /dev/null
+++ b/test/mitmproxy/script/test_reloader.py
@@ -0,0 +1,29 @@
+import mock
+from mitmproxy.script.reloader import watch, unwatch
+from test.mitmproxy import tutils
+from threading import Event
+
+
+def test_simple():
+    with tutils.tmpdir():
+        with open("foo.py", "wb"):
+            pass
+
+        script = mock.Mock()
+        script.filename = "foo.py"
+
+        e = Event()
+
+        def _onchange():
+            e.set()
+
+        watch(script, _onchange)
+        with tutils.raises("already observed"):
+            watch(script, _onchange)
+
+        with open("foo.py", "ab") as f:
+            f.write(".")
+
+        assert e.wait(10)
+
+        unwatch(script)